The present technique relates generally to a system and method of operating an engine and, more specifically, to a system and method for controlling the engine to enable use of a variety of different fuels with the engine.
Internal combustion engines are generally designed for one specific fuel. In general, internal combustion engines may be classified as either compression-ignition or spark-ignition engines. A common compression-ignition engine is a diesel engine, and a common spark-ignition engine is a gasoline engine. Engines also may be classified as either two-stroke or four-stroke. A four stroke engine includes an intake stroke, a compression stroke, a power stroke, and an exhaust stroke. During the intake stroke, the engine introduces fuel and air into a cylinder as its respective piston moves away from top dead center (TDC) in the cylinder. During the compression stroke, the piston moves toward TDC in the cylinder, thereby compressing the fuel/air mixture until ignition. The ignition occurs due to a spark (e.g., a spark plug) in a spark-ignition engine. In contrast, the ignition occurs due to the heat of compression and/or a glow plug in a compression-ignition engine. During the power stroke, the combustion of the fuel/air mixture causes significant heat and pressure in the cylinder, thereby driving the piston away from TDC and creating mechanical output power through the crankshaft, transmission, and so forth. During the exhaust stroke, the piston moves back toward TDC, thereby forcing the exhaust out of the cylinder. A two stroke engine operates by combining the power stroke with the exhaust stroke, and by combining the intake stroke with the compression stroke.
In each of these engines, a variety of parameters affect the engine performance, fuel efficiency, exhaust pollutants, and so forth. Exhaust pollutants include carbon oxides (e.g., carbon monoxide), nitrogen oxides (NOx), sulfur oxides (SOx), unburnt hydrocarbons (HC), and particulate matter (PM). Furthermore, each engine typically has design limits, such as speed, flow rate, temperature, and pressure, associated with the various components. For example, the design limits may include in-cylinder peak firing pressure (PFP), pre-turbine temperature (PTT) of a turbocharger, and turbocharger speed (TRBSPD) of the turbocharger. A specific design limit of a turbocharger is a choke line, which often represents a threshold limit in the air flow rate or pressure ratio between a compressor inlet and exit due to design constraints in the size of inlets, outlets, passages, and so forth. These engine parameters (e.g., PFP, PTT, and TRBSPD) should be maintained within design limits to avoid failure of the engine power assembly and turbocharger. Also, the compressor choke condition should be avoided to reduce the possibility of turbocharger failure.
Unfortunately, each engine is typically designed to work with a single specific fuel. Thus, any change in the fuel for these engines would result in a variety of problems and potential damage due to the different fuel characteristics, such as viscosity, compressibility, density, lower heating value (LHV), and so forth. For example, the different fuel characteristics may have a negative impact on the engine performance, fuel efficiency, and exhaust pollutants. Even worse, the different fuel characteristics may cause one or more engine components or parameters to exceed their design limits, thereby potentially causing damage and downtime. In one example, a fuel having a lower compressibility and a higher viscosity than a fuel intended for the engine would likely lead to a higher maximum fuel injection pressure, which could lead to failure of components in the fuel injection system if design limits are exceeded. In another example, a fuel having a smaller lower heating value (LHV) than a fuel intended for the engine would likely lead to greater fueling injected per stroke, thereby leading to higher injection and combustion durations. As a result, the smaller lower heating value (LHV) would likely cause a higher specific fuel consumption (SFC) and, thus, a higher fueling cost. These are merely some examples of the effects of utilizing a different fuel than intended for the particular engine.